CCL:G: Broken Symmetry Singlet Excited State

["Cristian V. Diaconu" <cvdiaconu*o*rice.edu>]

 Sent to CCL by: "Cristian V. Diaconu" [cvdiaconu~!~rice.edu]
 Hello Sue,
The total energy reported by Gaussian is not for 'annihilated' wave
 function, but
 for the single determinant that it uses in the Kohn-Sham scheme (for
 DFT there
 isn't really any wave function).  There are ways to extract the energy
 of the pure
 singlet from the broken symmetry state, but for DFT they only work in
 certain
 cases.  Please look at discussions in:
 J. Chem. Phys. 121, 10026 (2004)
 J. Chem. Phys. 74, 5737 (1981)
 Coord. Chem. Rev. 238–239, 187 (2003)
C. J. Cramer, in Essentials of Computational Chemistry. Theories and
 Models.
 (Wiley, Chichester, 2002), Chap. 14.4, pp. 456 – 459.
For example, for a molecule with two unpaired electrons on two sites
 which
 interact weakly (e.g., H2 molecule stretched, with a large bond length,
 say 10
 Angstroms), if <S^2> ~ 1,
 E(singlet) = 2 E(broken sym) - E(triplet)
I hope this helps.  If you have further questions, please include a
 little detail
 on the system you are looking at.
 Best regards,
 Chris
 Sue L chsue2004(~)yahoo.com wrote:
>  Sent to CCL by: "Sue  L" [chsue2004..yahoo.com]
> Hi,
>  
>  I am running a DFT open-shell singlet calculation using Gaussian 03 to
>  obtain a broken symmetry singlet excited state. Does anyone know whether the
>  electronic energy calculated at the end based on the annihilated wave function
>  or not?
>  
>  Thank you very much!
>  Best regards,
> Sue>
>  
 --
 Cristian V. Diaconu
 Postdoctoral Research Associate
 Department of Chemistry - MS60
 Rice University
 PO Box 1892
 Houston, TX 77251-1892
 Phone: 713-348-3734
 Email: cvdiaconu:-:rice.edu